next up previous 264
Next: MinAxes - Minimum number of Frame axes to match
Up: AST Attribute Descriptions
Previous: MaxAxes - Maximum number of Frame axes to match


MeshSize - Number of points used to represent the boundary of a Region

Description:
This attribute controls how many points are used when creating a mesh of points covering the boundary or volume of a Region. Such a mesh is returned by the AST_GETREGIONMESH method. The boundary mesh is also used when testing for overlap between two Regions: each point in the bomdary mesh of the first Region is checked to see if it is inside or outside the second Region. Thus, the reliability of the overlap check depends on the value assigned to this attribute. If the value used is very low, it is possible for overlaps to go unnoticed. High values produce more reliable results, but can result in the overlap test being very slow. The default value is 200 for two dimensional Regions and 2000 for three or more dimensional Regions (this attribute is not used for 1-dimensional regions since the boundary of a simple 1-d Region can only ever have two points). A value of five is used if the supplied value is less than five.
Type:
Integer.
Class Applicability:
Region
All Regions have this attribute.
CmpRegion
The default MeshSize for a CmpRegion is the MeshSize of its first component Region.
Stc
The default MeshSize for an Stc is the MeshSize of its encapsulated Region.


next up previous 264
Next: MinAxes - Minimum number of Frame axes to match
Up: AST Attribute Descriptions
Previous: MaxAxes - Maximum number of Frame axes to match

AST A Library for Handling World Coordinate Systems in Astronomy
Starlink User Note 210
R.F. Warren-Smith & D.S. Berry
24th May 2011
E-mail:ussc@star.rl.ac.uk

Copyright (C) 2009 Science \& Technology Facilities Council